There are a number of problems known in the field of optical communications, which concern regulating power of optical transmission in case of a fiber cut.
One of the problems is shutting down or reducing the power of an optical amplifier producing a light signal in the case of fiber cut or other hazardous events in the optical line transmitting the signal.
In point to point optical applications, where only amplifiers can be inserted between two terminal points, a fiber cut in any section of the optical link would allow the shut down of the whole link between the terminal stations.
In so-called Optical Ring, Chain, Mesh and other advanced network configurations every site can possibly contain either optical amplifiers or Optical Add Drop Multiplexers (OADM), or both. In the advanced network configurations, an optical trail may start and terminate at any site according to a customer's use. This fact rises a major survivability problem which never existed in the original point to point applications. In such configurations, a fiber cut in a span/section beyond the end points of a specific optical trail must not have any effect on the performance of any such optical trail. Usually, control systems handling optical transmission in the Ring and Chain configurations take care of the above problem.
Some of the presently used systems for DWDM networks introduce a so-called channel count mechanism. This mechanism transmits the number of active channels in the link to all the amplifiers in that link so they can modify their output power accordingly. In order to maintain balance in such a system, the number of channels dropped at a particular node should be approximately equal to the number of channels added at this node. However, this mechanism reacts incorrectly to events such as a fiber cut in a specific span of a link with OADMs (Optical Add Drop Multiplexers). Indeed, a fiber cut drastically changes the actual number of channels at more than one successive nodes, so the output power of the amplifiers in the link will not be correctly adjusted. The erroneous adjustment will most likely cause a degradation in optical performance of the system.
U.S. Pat. No. 6,072,601 describes an optical fiber amplifier capable of determining a number of optical channels actually inputted to it, thereby allowing, through self-control, both optimum operation conditions in accordance with the number of transmission channels, and the maintenance of the transmission performance. The optical fiber amplifier comprises an optical signal amplifier and a control circuit. The control circuit section comprises a branch circuit that branches off and extracts a portion of the transmitted optical signal power, and a channel counter that inputs a portion of the branched optical signal power and based on that counts the number of channels of the transmitted optical signals. The control circuit controls the amplification factor of the optical signal amplifier in accordance with the number of channels counted at the channel counter. The system counts the channels on the ad-hoc basis but is unable to predict the number of active optical channels in case of a fiber cut, which would be important to prevent ill effects of transient periods in the network until the channel count mechanism is updated.
Presently, there is no known methods/systems which dynamically count channels and adjust power in an optical communication system so, that occurrence of a fiber cut would not lead to an unbalancing of the system.